Catalyst and process for the preparation of hydrocarbons

ABSTRACT

The invention provides a process for the production of mainly C 5 + hydrocarbons, which process involves contacting carbon monoxide and hydrogen at a temperature in the range of from about 180° C. to about 270° C. and elevated pressure in the presence of a catalyst composition having cobalt, manganese and at least one of rhenium and/or ruthenium on a titania carrier. The invention also relates to a catalyst composition having cobalt, manganese and rhenium on a titania carrier.

FIELD OF THE INVENTION

The present invention relates to a catalyst and process for thepreparation of hydrocarbons from synthesis gas.

BACKGROUND OF THE INVENTION

The preparation of hydrocarbons from a gaseous mixture comprising carbonmonoxide and hydrogen (synthesis gas) by contacting the mixture with acatalyst at elevated temperature and pressure is well known in the artand is commonly referred to as Fischer-Tropsch synthesis.

Catalysts that may be suitably used in a Fischer-Tropsch synthesisprocess typically contain one or more catalytically active metals fromGroups 8 to 10 of the Periodic Table of the Elements. In particular,iron, nickel, cobalt and ruthenium are well known catalytically activemetals for such catalyst and may be optionally combined with one or moremetal oxides and/or metals as promoters. Cobalt has been found to be themost suitable for catalysing a process in which synthesis gas isconverted to primarily paraffinic hydrocarbons containing 5 or morecarbon atoms. In other words, the C₅+ selectivity of the catalyst ishigh.

Similar catalyst compositions are also known in other fields includingJP-A-404122454 which describes an exhaust gas purification catalystcomprising an active platinum group element such as ruthenium, rubidium,palladium and platinum or a metal oxide such as chromium, manganese,cobalt and nickel on an alumina, silica, titania, silica-titania oralumina-titania carrier. Catalysts of the invention are fitted in anexhaust gas purification catalytic converter and may be used incontrolling emissions from gasoline engines.

U.S. Pat. No. 5,134,109 provides a catalyst for the steam reforming ofhydrocarbons, which comprises at least one metal from rhodium andruthenium and at least one metal from cobalt and manganese deposited ona carrier which is preferably zirconia or stabilised zirconia.

JP-A-60064631 discloses a catalyst comprising an iron group metal suchas cobalt and iron, a platinum group metal such as ruthenium, rhodium,palladium, platinum and iridium, and manganese oxide, supported on acarrier comprising titanium oxide. JP-A-60064631 further discloses amethod for the production of high calorie gas containing hydrocarbons of1-4 carbons for use as fuels, from low calorie gas containing a mixtureof hydrogen, carbon monoxide and optionally carbon dioxide.

JP-A-60064631 is primarily concerned with a method for the production ofmethane and C₂₋₄ hydrocarbons and does not concern itself in any waywith increasing % C₅+ selectivity during the conversion of low caloriegas. Indeed, it can seen from Example 2 therein, which is the onlyexample of conversion of a simple CO/H₂ mixture, that the treatment of amixture of 3 parts H₂ and 1 part CO in the presence of a catalystcomposition comprising 10%. Co, 6% Mn₂O₃ and 2% Ru on a titaniumcarrier, results in 74.6% CH₄, 7.3% C₂H₆, 5.5% C₃H₈, 2.6% C₄H₁₀ and10.0% CO₂ (by % volume), i.e. the presence of C₅+ hydrocarbons was notdetected. This conversion was effected at 320° C., and although thebroadest temperature range disclosed for the process is 150 to 400° C.,it is stated that the preferred range is 260 to 350° C.

Although, U.S. Pat. No. 4,568,663 describes a rhenium-promoted cobaltcatalyst on an inorganic oxide support which is preferably titania,which catalyst may be employed in production of hydrocarbons by both FTsynthesis and the conversion of methanol, as being highly active, thisdisclosure is discussed in column 2, lines 19 to 35, of U.S. Pat. No.4,857,559, and contrasted with the corresponding alumina-supportedcatalyst, which has significantly higher activity.

Much research effort has been directed to finding catalysts having ahigher C₅+ selectivity than known catalysts at the same or higheractivity.

U.S. Pat. No. 4,857,559 concerns the addition of rhenium to cobalt on anumber of common supports including alumina, silica, titania, chromia,magnesia and zirconia and a process for the FT synthesis of hydrocarbonsusing said catalyst. However, it is recognised therein (e.g. column 4,lines 54 to 59 and column 15, lines 51-55) that whilst supports otherthan alumina may be used, such supports produce catalysts with muchlower activities. It is found in U.S. Pat. No. 4,857,559 that thehydrocarbon yield obtained by the addition of rhenium toalumina-supported cobalt catalyst is greater than the correspondingtitania-supported catalyst. In particular, the FT conversion ofsynthesis gas into hydrocarbons show lower % CH₄ selectivity, higher %CO conversion and higher C₂+ selectivity for rhenium-promoted cobaltcatalysts on alumina, than for similar catalysts on titania (Table 1).

TABLE 1 Example % CO % Selectivity No. % Co % Re Support Conversion C₂+CH₄ CO₂  8 12 1 Al₂O₃ 33 87.7 11.4 0.9 30 12 — TiO₂* 11 87.6 11.8 0.6 3112 1 TiO₂* 17 86.5 12.8 0.7 32 12 — TiO₂** 11 87.6 11.7 0.7 33 12 1TiO₂** 17 85.8 13.5 0.7 *support calcined at 500° C. **support calcinedat 600° C.

Based on the above disclosure, the person skilled in the art wouldclearly deduce that TiO₂ should be avoided as catalyst carrier forrhenium/cobalt combinations in favour of Al₂O₃.

Fischer-Tropsch synthesis of hydrocarbons produces a number ofby-products such as carbon dioxide, water and gaseous C₁₋₄ hydrocarbons.

As well as improving % CO conversion, it is of prime importance to beable to adjust the product slate in any given Fischer-Tropsch reaction,to satisfy individual requirements such as increased % C₅+ selectivityand reduced CH₄ and CO₂ production.

It is highly desirable to reduce the amount of carbon dioxide evolvedduring Fischer-Tropsch synthesis of hydrocarbons for both economic andenvironmental reasons. It is particularly desirable to restrict thelevel of carbon dioxide by-product in such process to less than 2% v/v,preferably less than 1% v/v.

Of prime importance is that any methodologies employed for a reductionin carbon dioxide selectivity in Fischer-Tropsch synthesis, do not causea concomitant reduction in C₅+ hydrocarbon selectivity.

It can be seen from Table 1, that whilst the addition rhenium to acobalt catalyst on titania gives a modest increase in activity from 11%carbon monoxide conversion to 17% carbon monoxide conversion, the C₂+selectivity is reduced and the CO₂ selectivity is equal or increasedcompared to the corresponding unpromoted catalyst.

WO-A-97/00231 relates to a catalyst comprising cobalt and manganeseand/or vanadium supported on a carrier wherein the cobalt:(manganese+vanadium) atomic ratio is at least 12:1.

Said catalyst exhibits higher C₅+ selectivity and higher activity whenused in the Fischer-Tropsch synthesis of hydrocarbons, compared tocatalysts containing cobalt only, or containing a relatively higheramount of manganese and/or vanadium. Preferred carriers include titania,zirconia and mixtures thereof.

It is highly desirable not only to increase further the C₅+ selectivityof such cobalt manganese catalysts, but also to reduce their carbondioxide selectivity.

It has now been surprisingly found that the addition of small quantitiesof rhenium and/or ruthenium to cobalt-manganese catalyst compositionscan not only cause reductions in carbon dioxide selectivity, but canalso have dramatic effects on the product slate obtained from FThydrocarbon synthesis reactions.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a process for the productionof mainly C₅+ hydrocarbons comprising contacting carbon monoxide andhydrogen at a temperature in the range of from about 180° C. to about270° C. and elevated pressure in the presence of a catalyst compositioncomprising cobalt, manganese and at least one of rhenium and/orruthenium on a titania carrier.

DETAILED DESCRIPTION OF THE INVENTION

According to another aspect, the present invention provides a catalystcomposition comprising cobalt, manganese and rhenium on a titaniacarrier.

By “mainly” in the present invention is meant an amount greater thanabout 80 wt. % based on the paraffinic hydrocarbon and carbon dioxidedistribution.

By “product slate” in the present invention is meant the overall productdistribution resulting from Fischer-Tropsch synthesis of hydrocarbons,i.e. the relative amounts of C₁₋₄ hydrocarbons, C₅+ hydrocarbons, waterand carbon dioxide present in the product mixture.

The rutile:anatase weight ratio in the titania carrier is not limited inthe present invention, however said ratio may conveniently be less thanabout 2:3, as determined by ASTM D 3720-78.

The titania carrier may be prepared by any method known in the art,however it is particularly preferred that the titania carrier isprepared in the absence of sulphur-containing compounds. An example ofsuch a preparation method involves flame hydrolysis of titaniumtetrachloride. It will be appreciated that the titania powder derivedfrom such a preparation method may not be of the desired size and shape.Thus, usually a shaping step is required to prepare the carrier. Shapingtechniques are well known to those skilled in the art and includepelletising, extrusion, spray-drying, and hot oil dropping methods.

Titania is available commercially and is well-known as a material foruse in the preparation of catalysts or catalyst precursors.

As an alternative or in addition to titania, the mixture may comprise atitania precursor. Titania may be prepared by heating titaniumhydroxide. As the heating progresses, titanium hydroxide is convertedvia a number of intermediate forms and the successive loss of a numberof water molecules into titania. For the purpose of this specification,the term “titania precursor” is to be taken as a reference to titaniumhydroxide or any of the aforementioned intermediate forms.

Catalysts that may be used in the process of present inventionpreferably contain from about 5 wt. % to about 30 wt. % of Co based onthe total weight of the catalyst composition, more preferably from about10 wt. % to about 25 wt. % of Co based on the total weight of thecatalyst composition, and most preferably about 15 wt. % to about 25 wt.% of Co based on the total weight of the catalyst composition.

Catalysts that may be used in the process of present inventionpreferably contain from about 0.01 wt. % to about 5 wt. % of Mn based onthe total weight of the catalyst composition, more preferably from about0.01 wt. % to about 1.5 wt. % of Mn based on the total weight of thecatalyst composition.

Catalysts that may be used in the process of present inventionpreferably contain from about 0.01 wt. % to about 5 wt. % each ofrhenium and/or ruthenium based on the total weight of the catalystcomposition, more preferably from about 0.01 wt. % to about 1 wt. % eachof rhenium and/or ruthenium based on the total weight of the catalystcomposition, and most preferably from about 0.01 wt. % to about 0.5 wt.% each of rhenium and/or ruthenium based on the total weight of thecatalyst composition.

Catalysts that may be used in the process of the present invention mayfurther comprise up to about 20 wt. % of a binder material such asalumina or silica based on the total weight of the catalyst composition,preferably up to about 10 wt. % of a binder material such as alumina orsilica based on the total weight of the catalyst composition.

The pore size and volume of the catalyst composition prior to activationare not limited in the present invention. The pore volume mayconveniently be in the range of from about 0.1 cm³/g to about 0.8 cm³/g,preferably in the range of from about 0.15 cm³/g to about 0.7 cm³/g,more preferably in the range of from about 0.2 cm³/g to about 0.5 cm³/g.

The catalyst of the present invention may be prepared by methods knownto those skilled in the art, such as by precipitating the catalyticallyactive compounds or precursors onto the carrier; spray-coating, kneadingand/or impregnating the catalytically active compounds or precursorsonto the carrier; and/or extruding one or more catalytically activecompounds or precursors together with carrier material to preparecatalyst extrudates.

It will be appreciated by those skilled in the art that the mostpreferred method of preparation may vary, depending e.g. on the desiredsize of the catalyst particles. It belongs to the skill of the skilledperson to select the most suitable method for a given set ofcircumstances and requirements.

Extrusion may be effected using any conventional, commercially availableextruder. In particular, a screw-type extruding machine may be used toforce the mixture through the orifices in a suitable dieplate to yieldextrudates of the desired form. The strands formed upon extrusion may becut to the desired length.

After extrusion, the extrudates are dried. Drying may be effected at anelevated temperature, preferably up to about 500° C., more preferably upto about 300° C. The period for drying is typically up to about 5 hours,more preferably from about 15 minutes to about 3 hours.

The extruded and dried catalyst composition may be calcined. Calcinationis effected at elevated temperature, typically in the range of fromabout 200° C. to about 900° C., preferably at a temperature in the rangeof from about 400° C. to about 750° C., more preferably in the range offrom about 500° C. to about 650° C. The duration of calcinationtreatment is conveniently from about 5 minutes to several hours,preferably from about 15 minutes to about 4 hours.

Conveniently, the calcination treatment is carried out in anoxygen-containing atmosphere, preferably air. It will be appreciatedthat, optionally, the drying step and the calcining step may becombined.

A preferred method of preparing the catalyst according to the presentinvention is by impregnating the catalytically active compounds orprecursors onto a carrier. Thus, typically the carrier is impregnatedwith a solution of a cobalt compound, a solution of a rhenium and/orruthenium compound and a solution of a manganese compound. Preferably,the carrier is impregnated simultaneously with the respective metalcompounds. Thus, according to a preferred embodiment, the process forpreparing the catalyst for use in the process of the present inventioncomprises co-impregnating the carrier with a solution of a cobaltcompound, a solution of a rhenium and/or ruthenium compound and asolution of a manganese compound.

A further preferred method of preparing the catalyst according to thepresent invention is by mixing some of the catalytically activecompounds or precursors with the carrier, followed by extruding theresulting mixture, followed by drying and calcining the extrudate,followed by impregnating with further catalytically active compounds orprecursors to prepare catalyst extrudates for use in the process of thepresent invention.

Thus, typically the carrier is mixed with a cobalt compound and amanganese compound and water followed by extrusion of the resultingmixture, and after drying and calcining, followed by impregnation with asolution of a rhenium and/or ruthenium compound to prepare catalystextrudates for use in the process of the present invention. Preferably,the carrier is mixed simultaneously with the cobalt and manganesecompounds.

Thus, according to a preferred embodiment, the process for preparing thecatalyst for use in the process of the present invention comprisesco-extruding the carrier with a cobalt compound and a manganesecompound, followed by impregnating the extrudate with a solution of arhenium and/or ruthenium compound.

Examples of suitable cobalt compounds that may be used in thepreparation of said catalyst include one or more of cobalt hydroxide,cobalt oxide, cobalt carbonyl, halides such as cobalt chloride(hexahydrate or anhydrous), inorganic acid salts such as cobaltsulphate, cobalt nitrate or cobalt carbonate, and organic acid saltssuch as cobalt acetate and cobalt formate. Preferred cobalt compoundsinclude cobalt hydroxide, cobalt carbonate and cobalt nitrate.

Examples of suitable rhenium compounds that may be used in thepreparation of said catalyst include one or more of rhenium oxide,rhenium chloride, rhenium carbonyl, ammonium perrhenate and perrhenicacid. The preferred rhenium compound is ammonium perrhenate.

Examples of suitable ruthenium compounds that may be used in thepreparation of said catalyst include one or more of a ruthenium halidesuch as ruthenium chloride or ruthenium iodide, a ruthenic halide orsalt thereof, for example ruthenic chloride, ammonium ruthenic chloride,sodium ruthenic chloride, potassium ruthenic chloride, a ruthenium oxidesuch as ruthenium di or tetraoxide, a ruthenic acid salt such aspotassium ruthenate or sodium ruthenate, an organic ruthenium compoundsuch as ruthenium carbonyl, ruthenium nitrosyl nitrate. The preferredruthenium compound is ruthenium nitrosyl nitrate.

Examples of suitable manganese salts that may be used in the preparationof said catalyst include one or more of manganese hydroxide, manganeseoxide, halides such as manganese chloride, inorganic acid salts such asmanganese sulphate, manganese nitrate or manganese carbonate, andorganic acid salts such as manganese acetate and manganese formate.Preferred manganese compounds include manganese hydroxide, manganesenitrate and manganese acetate.

The impregnation treatment is typically followed by drying and,optionally, calcining. Drying is typically carried out at a temperaturein the range of from about 50° C. to about 300° C. for up to about 24hours, preferably from about 1 to about 4 hours.

Calcination is typically carried out at a temperature in the range offrom about 200° C. to about 900° C., preferably, in the range of fromabout 250° C. to about 700° C. The duration of the calcination treatmentis typically from about 0.5 to about 24 hours, preferably from about 1to about 4 hours. Suitably, the calcination treatment will normally behigher than the average temperature during the drying treatment.

When in use, the catalyst for the process of the present invention maycontain at least part of the cobalt in its metallic form.

Therefore, it is normally advantageous to activate the catalyst prior touse by a reduction treatment, in the presence of hydrogen at elevatedtemperature. Typically, the reduction treatment involves treating thecatalyst at a temperature in the range of from about 100° C. to about450° C. for about 1 to about 48 hours at elevated pressure, typicallyfrom about 0.1 MPa to about 20.0 MPa (1 to 200 bar abs.). Pure hydrogenmay be used in the reduction treatment, but it is usually preferred toapply a mixture of hydrogen and an inert gas, such as nitrogen. Therelative amount of hydrogen present in the mixture may range frombetween 0% to about 100% by volume.

According to one preferred embodiment, the catalyst is brought to thedesired temperature and pressure level in a nitrogen gas atmosphere andsubsequently, the catalyst is contacted with a gas mixture containingonly a small amount of hydrogen gas, the rest being nitrogen gas. Duringthe reduction treatment, the relative amount of hydrogen gas in the gasmixture is gradually increased up to about 50% or even about 100% byvolume.

If possible, it is preferred to activate the catalyst in situ i.e.inside the reactor. WO-A-97/17137 describes an in situ catalystactivation process which comprises contacting the catalyst in thepresence of hydrocarbon liquid with a hydrogen-containing gas at ahydrogen partial pressure of at least about 1.5 MPa (15 bar abs.),preferably at least about 2.0 MPa (20 bar abs.), more preferably atleast about 3.0 MPa (30 bar abs.). Typically, in this process thehydrogen partial pressure is at most about 20 MPa (200 bar abs.).

It is advantageous to rejuvenate spent catalyst, i.e. catalyst that haslost at least part of the initial activity of an activated freshcatalyst, by subjecting it to a hydrogen strip or an ROR treatment.Conveniently, the ROR treatment involves the steps, in sequence, ofreduction with a hydrogen-containing gas, oxidation with anoxygen-containing gas, and reduction with a hydrogen-containing gas.

The process of the present invention is preferably carried out at atemperature in the range of from about 200° C. to about 250° C. Thepressure is typically in the range of from about 0.5 MPa to about 15.0MPa (5 to 150 bar abs.), preferably in the range of from about 1.0 Mpato about 8.0 MPa (10 to 80 bar abs.), in particular from about 1.0 Mpato about 6.0 MPa (10 to 60 bar abs.).

Hydrogen and carbon monoxide (synthesis gas) may be conveniently fed tothe process at a molar ratio in the range of from 1 to 2.5.

The gas hourly space velocity (GHSV) of the synthesis gas in the processof the present invention may vary within wide ranges and is typically inthe range of from about 400 to about 10000 N1 l⁻¹h⁻¹, for example fromabout 400 to about 4000 N1 l³¹ ¹h⁻¹. The term GHSV is well known in theart, and relates to the volume of synthesis gas in N1, i.e. litres atstandard temperature and pressure (STP) conditions (0° C. and 1 barabs.), which is contacted in one hour with one litre of catalystparticles, i.e. excluding interparticular void spaces for slurryreactions. In the case of a fixed catalyst bed, the GHSV may also beexpressed as per litre of catalyst bed, i.e. including interparticularvoid space.

The process of the present invention for the preparation of hydrocarbonsmay be conducted using a variety of reactor types and reaction regimes,for example a fixed bed regime, a slurry phase regime or an ebullatingbed regime. It will be appreciated that the size of the catalystparticles may vary depending on the reaction regime they are intendedfor. It belongs to the skill of the skilled person to select the mostappropriate catalyst particle size for a given reaction regime.

Further, it will be understood that the skilled person is capable ofselecting the most appropriate conditions for a specific reactorconfiguration and reaction regime. For example, the preferred gas hourlyspace velocity may depend upon the type of reaction regime that is beingapplied. Thus, if it is desired to operate the hydrocarbon synthesisprocess with a fixed bed regime, preferably the gas hourly spacevelocity is chosen in the range of from about 500 to about 2500 N1l⁻¹h⁻¹. If it is desired to operate the hydrocarbon synthesis processwith a slurry phase regime, preferably the gas hourly space velocity ischosen in the range of from about 1500 to about 7500 N1 l⁻¹h⁻¹.

The present invention is illustrated by the following Examples, whichshould not be regarded as limiting the scope of the invention in anyway.

EXAMPLES Example 1 (Comparative)

A mixture was prepared containing 112.5 g of commercially availabletitania powder (p25 ex. Degussa), 49.5 g of commercially available Co(OH)₂ powder, 8.2 g Mn(Ac)₂·4H₂O (wherein “Ac” represents acetate) and45 g water. The mixture was kneaded for 30 minutes. The mixture wasshaped by means of an extruder.

The extrudates were dried for 2 hours at 120° C. and subsequentlycalcined for 2 hours at 500° C.

The catalyst (I) thus produced, contained 22% by weight of cobaltcompounds, expressed as cobalt metal, and 1.2% by weight of manganesecompounds, expressed as manganese metal, based on the total weight ofthe catalyst composition.

Example 2

A portion of catalyst (I) was impregnated with an aqueous solution ofammonium perrhenate (NH₄ReO₄)

The extrudates were dried for 2 hours at 120° C. and calcined for 2hours at 500° C.

The catalyst (II) thus produced, contained 22% by weight of cobaltcompounds, expressed as cobalt metal, 1.2% by weight of manganesecompounds, expressed as manganese metal, and 0.18% by weight of rheniumcompounds, expressed as rhenium metal (9.7×10⁻⁶ mol Re/gram catalyst),based on the total weight of the catalyst composition.

Example 3

A portion of catalyst (I) was impregnated with an aqueous solution ofruthenium nitrosyl nitrate (Ru(NO)(NO₃)_(x)(OH)_(y), x+y=3).

The extrudates were dried for 2 hours at 120° C. and calcined for 2hours at 500° C.

The catalyst (III) thus produced, contained 22% by weight of cobaltcompounds, expressed as cobalt metal, 1.2% by weight of manganesecompounds, expressed as manganese metal, and 0.10% by weight ofruthenium compounds, expressed as ruthenium metal (9.9×10⁻⁶ mol Ru/gramcatalyst).

Example 4

Catalyst testing was performed according to the method described inWO-A-97/00231. Catalysts I, II, and III were tested in a process for thepreparation of hydrocarbons. Microflow reactors A, B, and C, containing10 ml of catalysts I, II, and III respectively, in the form of a fixedbed of catalyst particles were heated to a temperature of 260° C., andpressurised with a continuous flow of nitrogen gas to a pressure of 0.2MPa (2 bar abs.). The catalysts were reduced in situ for 24 hours with amixture of nitrogen and hydrogen gas. During reduction, the relativeamount of hydrogen in the mixture was gradually increased from 0% to100%. The water concentration in the off-gas was kept below 3000 ppmv.

Following reduction, the pressure was increased to 2.6 MPa (26 barabs.). The reaction was carried out with a mixture of hydrogen andcarbon monoxide at a H₂/CO ratio of 1.1:1. The GHSV amounted to 800 Nll⁻¹h⁻¹. The reaction temperature is expressed as the weighted averagebed temperature (WABT) in ° C. The space time yield (STY), expressed asgrammes hydrocarbon product per litre catalyst particles (including thevoids between the particles) per hour, the C₅+ selectivity, expressed asa weight percentage of the total hydrocarbon product, and the CO₂selectivity, expressed as a molar percentage of the CO converted, weredetermined for each experiment after 50 hours of operation. The resultsare set out in Table I.

TABLE I Catalyst I II III WABT (° C.) 209 202 206 STY (g l_(cat) ⁻¹h⁻¹)100 100 100 C₅+ selectivity (%) 92 95 94 CO₂ selectivity (%) 1.2 1.0 0.8

It will be appreciated that, in addition to the reduction in CO₂selectivity, the activity and C₅+selectivity of both catalysts II andIII, according to the invention, is much better than that of catalyst I.

We claim:
 1. A process for the production of mainly C₅+ hydrocarbons,which process comprises: contacting carbon monoxide and hydrogen at atemperature in the range of from about 180° C. to about 270° C. andelevated pressure in the presence of a catalyst composition comprisingcobalt, manganese and at least one of rhenium and/or ruthenium on atitania carrier wherein the process has a selectivity for carbon dioxideless than or equal to 1%.
 2. The process of claim 1, wherein thecatalyst contains from a at 5 wt. % to about 30 wt. % of Co based on thetotal weight of the catalyst composition and wherein the catalystcontains from about 0.01 wt. % to about 5 wt. % Mn based on the totalweight of the catalyst composition.
 3. The process of claim 1, whereinthe catalyst contains about 0.01 wt. % to about 5 wt. % each of rheniumand/or ruthenium based on the total weight of the catalyst composition.4. The process of claim 1, wherein the temperature is in the range fromabout 200° C. to about 250° C.
 5. The process of claim 1, wherein saidprocess is carried out under fixed bed conditions.